They also counted the frequency of other terms, such as "H1N1" and "vaccine".

Kostkova's team is working together with the European Centre for Disease Prevention and Control (ECDC) and Britain's National Health Service (NHS) in the run-up to the 2012 Olympic Games in London.

Twitter would enable the NHS, for example, to better assess resources and provide visitors with information such as the nearest doctor, dentist or emergency services.

Source of rumour

A report released yesterday by the World Health Organization found that the Internet had a disruptive impact on the handling of the flu pandemic by fanning speculation and rumour.

WHO influenza chief Dr Keiji Fukuda told 29 health experts reviewing the international response to the pandemic that the Internet had added a new dimension to flu alerts over the past year.

While it meant information about swine flu became more widely available, it also produced "news, rumours, a great deal of speculation and criticism in multiple outlets," including blogs, social networking and websites, he said.

"Anti-vaccine messaging was very active, made it very difficult for public health services in many countries," Fukuda said as a nine-month review of the A(H1N1) flu pandemic got under way.

Kostkova counters that monitoring Twitter messages would help recognise the population's worries and could be useful in detecting the start of an epidemic.

But she insists that existing disease surveillance systems were still better for monitoring the subsequent spread of an epidemic.